Diaphragm



- Patented Sept. 24, 1929 UNITED STATES PATENT OFFICE CLARENCE S. WICKES, F MERCHANTVILLE, NEW JERSEY, ASSIGNOR TO VICTOR DIAPHRAGM No Drawing. Application filed Dec-ember This invention relates to diaphragms and more particularly to diaphragms for use in reproducing sound.

Many substances have heretofore been employed for making sound reproducing diaphragms. For example, commercial aluminum has been suggested for making diaphragms for talking machine sound boxes.

In order to employ materials of this nature it is necessary that the metal be rolled into extremely thin sheets, a thin, light diaphragm being desired for the reproduction of high frequency sound waves. For example, frequencies on the order of 5,000 are involved when it is desired to reproduce the highest note of an orchestra.

Difiiculty is encountered in rolling commercialaluminum into thin sheets for use in making diaphragms due to the impurities therein. Moreover, holes frequently develop during the rolling process of the sheet which seriously affect the value of the latter as a diaphragm material. Commercial aluminum of the best grade contains from 0.18 to 0.40 per cent of iron and 0.29 to 0.40 per cent of silica, among other impurities. Because of these impurities it is extremely difficult to form a diaphragm of commercial aluminum which will reproduce the high frequency sound waves. The reproduction of high frequencies is essential in order that the quality characteristics determined by the high partials of low and medium register notes may be secured and also in order that the fundamentals of the high register may be faithfully reproduced.

It is recognized, however, that aluminum possesses many characteristics which render it highly useful as a diaphragm material, but in view of the difiicult-y heretofore experienced in securing a satisfactory diaphragm of this material, it has been proposed to substitute duralumin in place of aluminum. Considerable difiiculty and expense, however, is involved in rolling duralumin to the thickness required for diaphragm material and such thin sheets of duralumin are exceedingly diflicult to handle without fracture. I have discovered that the difiiculties heretofore experienced from the use of commercial alumi- 7, 1925. Serial No. 73,902.

num may be greatly diminished, if not elimmated, by employing aluminum which is in a substantially chemically pure state, and at the same time avoid much of the difficulty that has been experienced in the efforts to 5 substitute duralumin as a diaphragm material for aluminum.

An object of the present invention is to provide a diaphragm formed of chemically pure aluminum whereby a diaphragm of exceedingly light weight and extreme; thinness 1s secured which is capable of faithfully reproducing very high frequencies.

Other objects of the invention are to provide a high frequency diaphragm which may be inexpensively rolled; which is durable and not readily subject to corrosion, and which has a greater internal viscosity or resistance than diaphragms heretofore produced, such for example as those formed of duralumin; to provide a diaphragm with a less rigid outer periphery than those heretofore formed of commercial aluminum and duralumin; and to provide a diaphragm material wherein deeper fins may be pressed and which may be more readily seated in a mounting, such, for example, as a talking machine sound-box.

In accordance with the present invention, chemically pure aluminum, that is aluminum which is approximately 99.9 percent pure, is rolled into sheets in any suitable manner well known in the art, approximately 1/500 of an inch in thickness. This thickness may be varied, however, in accordance with the size or diameter of the diphragm'it is desired to produce. I have discovered that aluminum is capable of an increased efficiency as regards reproduction of highfrequency sound waves, is more durable and can be rolled into thinner sheets more inexpensively and satisfactorily than materials heretofore employed, if in a substantially chemically pure state, which at the present'state of the art may contain approximately 0 005 percent of iron, 0.005 percent of silicon, no silica, and ap- 95 proximately 0.007 percent of copper. As here,- in employed, the term chemically pure aluminum refers to such aluminum, for example, as is produced by the Hoopes proc- 'ess described in a paper The Electrolytic Refining of Aluminum by F. C. 'Frary (Transactions of the Americanv Electroglziegnical Society, Vol. XLVII, 1925, p.

After being rolled into sheets of desired thickness, the sheets are cut in any suitable manner, as by punching, into shapes of the desired size, and may be pressed into any suitable form. For example, fins may be pressed into the diaphragm to 'stren hen the same and enable the diaphragm to e of reducedthickness in order to favor low register notes.

By my discovery, after a series of experiments, t at improved results may be secured by the use of chemically pure aluminum, whereby said aluminum may be worked to a thinner sheet than has heretofore been secured, thus securing a lighter diaphragm and one which secures better high frequency reister, the difliculty and expense incident to orming a diaphragm of duralumin is obviated. Moreover, a lighter diaphragm is secured which has greater internal viscosity or resistance than a commercial aluminum diaphragm or one formed of duralumin, and which is therefore not so susceptible to rattles as a diaphragm formed of the materials mentioned above. Moreover, the diminution in the impurities, althpugh only a fraction of a percent, is productive of relatively large advantageous results which are entirely disproportionate to the change in actual composition.

From the above it will be seen that the use of chemicall purealuminum for forming diaphra s or talking machine sound boxes results 1n a diaphragm of increased efliciency, in that the range of frequencies that can be reproduced is greatl extended, while it is less fragile and less su ject to corrosion than commercial aluminum or duralumin.

Moreover, the use of chemically pure aluminum, which is a softer substance than either commercial aluminumor duralu'min, results in a decided saving in the rolling operation. It is to be expressly understood that the present invention is not limited to diaphragms for talking machine sound boxes and reference will be had to the appende claim for a definition of the limits of the invention.

WVhat is claimed is:

A diaphragm for reproducing sound waves which is formed from a rolled sheet of aluminum that contains not more than two-tenths percent of impurities and having high internal resistance.

In testimony whereof I have signed this specification.

CLARENCE S. WICKES. 

